From the point of view of performance, I think there's nothing like a good fixed blade. Folders are the next best thing, are legal to carry in more places (are more socially accepted as well) and in most cases are more conveniant to have on your person at all times, but are just inferior tools.
Yes, but no.
Yes, in that any sane knife enthusiast will almost always prefer a fixed blade to a folder no matter what the cutting task and no matter what the size. That's a no brainer.
But no, in that a tool that can't be carried as easily, is less likely to get carried, is more likely to cause problems when carried and that offers no massive advantages for a given size range is actually inferior in that context.
Context is really everything.
In the 3" (blade) and below size range, it's very hard to argue that a fixed blade offers significant advantages with the exception of industrial use, cleaning large game or high end carving. In these cases, the advantage is large grips combined with small blades for more control, not strength.
In the 4" (blade) and above size range, this issue is almost moot. At that point, the folder becomes a luggable or sheath carry tool, just a like a fixed blade and once deployed, the sheer size will be upsetting to most civilians (and rightly so) in most situations just as a full fixed blade will.
In that 3.5" to 4" (blade) length range though... While I can't use my Opinel #10 or Buck 110 as a pry bar to open a wooden crate, a) I would be very hesitant to do that with even the toughest 3.5" bladed fixed blade (too much leverage on too short of a fulcrum) and b) I can take those folders into nearly any social situation so long as I use discretion.
The end result is that a Buck 110 is a much more useful tool than, say a Buck 103 and a Opinel #10 is a much more useful tool than, say, a Mora. I have the Opinel #10 in my EDC day pack and don't think twice about it. The Mora would cause a stink.

EDC Back Ups by Pinnah, on Flickr